Co-Parenting Mayhem

8 is too young for a phone. Add in the abusive ex and you're giving ex tools to continue to abuse you.
He abused you, he's now doing it to your son. Your son's comments about your drinking and his behaviour shows he is being told inappropriate things.
I think you need to get a court order in place. Phone calls cab be twice a week at the exact same time, videocall, with you in the room. Anything inappropriate then you say bye and hang up.
You need to teach your son skills to trust his gut. Books like The Sky Is Red is good to get them to challenge what adults tell them and trust their gut. We pkay 'fact or opinion' and we do it about everything else except dad. Baked beans are the best food in the world- fact or opinion? And the kids question it. Now my 7 year old is starting to use those questioning skills on what daddy says. Everything is dad says is a fact in his dad's eyes which was really getting in the way of my relationship with the kids. It seems to be helping now.
Also, document all of this. The missed contact, what your son says that are adult issues. I think you seriously need to go.to court and get a Children's Arrangement Order so you have a Lives with Order and dad's behaviours are documented. The fact you have had third party worries and involvement is great.
I'd also consider looking at local charities and see what is on offer for play therapy. They will then work through these feelings with your son, help him to work through the crap that seems to be what dad is putting into his head.
I'm about to start the Freedom Project online- might be worth having a go yourself. You are so desensitised to yiur ex's antics that you doubt every move you make as a parent. I completely understand that feeling. Stay strong.
Really sorry you're dealing with this. I'm in a similar situation but the court order is my saving grace as he limits my ex's control over me and the kids. We have no phone calls as I said it wasn't helping the kids. Same as what you witness with your son. Wishing you and your son well!

Ok, your ex is a dick and I’m so sorry you’ve been through so much

however- this is not coparenting
I have told ex husband he needs to stay out of the rules I set in my household, respect me as his mother and not to give DS medicine when it is not needed.

if your son has a sore throat and wants Calpol, why ,don’t you just give him some? You are being unreasonable on this.
Don’t start monitoring phone calls, that will escalate issues and damage your relationship with your son
also, I don’t think it’s fair to punish your son for making arrangements with adults, is the adults who ought to be having boundaries around this, he is a very young and it is beyond him to manage this, especially if his father is being coercive about it. If you want to have set contact arrangements, go and get a child arrangements order.

This

The phone needs to go. Given what you have said about his dad’s behaviour I would also not let DS speak to him outside of contact times on my phone either. Less contact the better. Accept that your ex will always be abusive and as a result don’t give him an inch.

The phone needs to go.

That’s awful, this sounds like such a difficult situation and things to be going through.

Well it’s obvious your ex and his family have dripped poison in your son’s ear - I assume for years? I can predict your future with ease. He will get to a certain age and request he lives with his dad. You will feel compelled to agree and off he will go.

The phone needs to go and if Dad calls him on your phone you need to supervise the phone call and immediately intervene if necessary. Stick to the parenting plan.

That’s fair

That's not reasonable though if teh other parent is feeding into the child's demands. You can't show a united front with someone not willing to co-parent.

This is definitely not ok. I would say a few things - firstly he is far too young to have a phone. If he wants to speak to his dad when he’s with you, he can use your phone. Absolutely no way an 8 year old needs a phone. My 11 year old still doesn’t have a phone, but will get one (a non-smart phone only) when he goes to secondary school in September. You need a clear schedule with his dad that you both stick to. And you need to be a united front on things and for your son to know that he can’t play you off against each other. If mine said they get extra treats with their dad or something I’d be making sure they know that me and their dad are friends and talk about everything and that I know they are not being honest. It’s bad for your kid to end up in this position. Your son needs to see no signs of disagreement ever between you and his dad.

Take the phone away permanently and allow him a scheduled number of calls to his father each week which you supervise.

Take his phone away.
Let him use your phone when you’re in the room so you hear what he’s saying.
Speak to son and explain why he didn’t need medicine etc.

The phone goes. Simple as. He can’t be trusted with it and it’s causing issues for you. If he wants to speak to his dad he can use your phone.

Your ex is told that your rules and judgement apply during your time. He isn’t just to turn up at your door or make plans with an 8 year old without consulting you. Wouldn’t hurt to get some fixed court ordered plans in place to reinforce this if you havent already. Would also mean you have no need to speak to your ex.

Remain consistent and firm but loving with your ds. He doesn’t want to see you as the enemy and his dad as the hero who will rescue him from your rules. But he also needs to know that playing you off and being deliberately deceptive isn’t ok.

I think you need a more formalised child arrangements order which lays who has DS and when. You can't reason with unreasonable people so you have to have some rules and stick to them rigidly.

I used to keep a totally dry house because ex would tell people I kept alcohol in and drank a lot had the teachers sniffing me at pick ups and drop offs finally social services came over asking if I drank ex said I was a drinker I said no? my friend who was there laughed and told them she had known me for years I wasn't a drinker she had never even seen me take a sip they were puzzled then his (ex husbands step dad) slipped up and said i wasn't a drinker either ex was noted as a hostile parent and everyone moved on he was warned against time wasting he did his little "outraged concerned father" act and backed down

God that's infuriating - not on your side but on the side of the authorities who have looked at an abusive man and deemed him fit to take care of a child. I'd advise you to keep track of what's happening, record incidents etc in case you have to take action at a later stage. In the meantime you might want to have a serious (age appropriate) talk to your son about his dad. There may be behaviours he's experiencing that are confusing him/making him feel unsafe.

This is all perfectly normal. It's hard for.kids to regulate moving from one environment to another... but keep your rules the same and he'll get used to it.

Like others have said, if your Ex and your son cannot handle the phone responsibly then it's taken away. 8 isn't really old enough to have a phone IMO.

So take the phone, then when dad phones in a morning you can say sorry DS is busy getting ready for school. They don’t need to have such regular phone contact, is isn’t helping your DS

Take the phone off him for a day or two until he learns to use it as it was intended. Or make access to the phone only by asking you.

Have a bottle of "Medicine" available for days like this? just syrup or something. Give a spoonful, then after half an hour say "oh that's all cleared up then"