Having been through very similar with two boys now (11 and 16), both ASD/PDA, I would offer different advice (but I expect, in a thread where everyone has agreed with the punishment route for it to go down like a lead balloon 
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He sounds like a real mix of my two boys. The sociability of ds2, the obnoxiousness of ds1.
IMO (bearing in mind I can only go by what you've written), you suspect ASD, and there must be a very real possibility of this or other SEN for school to be considering an EHCP, it's very possible that the behaviour after school is the overflow following a day at school (coke bottle effect - shaken up throughout the day, it's only once home that the lid comes off)
You may find that the punishments you're suggesting make no difference, as DC with ASD can have great difficulty in understanding consequences, and he may assume you're stealing his things and the behaviour you're trying to modify will be increased, it may also be denying him a valuable way to wind down, the importance of which cannot be underestimated.
Ds1's speciality is disrespectful behaviour, but we have eventually worked out that this is his version of a meltdown, punishing has zero effect, the only thing that helps is to understand how awful he is feeling at those points and offer support or stay out of his way.
Once calm, we can talk about it, before that point he can't hear us or take in what we're saying.
Ds2 is the one who pushes boundaries constantly, we have learnt that pushing back makes him more defiant and difficult, and what works best is teaching him (and us) to compromise - the book The Explosive Child is excellent for this. The thing is, if he's never going to listen, it's better to show him that you can listen to him as well. With us it does mean being prepared to accept that ds simply cannot accept rules that he doesn't see the point of (but this is the PDA side).
As for the phone, this is something you could use as a bargaining tool, as he'll see the benefit. I wouldn't have a child on any sort of contract, but you could offer a fixed sum every week (£5? - £10?) reliant on him at least trying not to,be disrespectful to you.
If he's disrespectful in school, he may not understand why you're punishing him at home as well.
I would talk to teachers and tell them how you handle it and what works, the rest is up to them (I have a NT daughter, we handle things differently with her because it works! I'm not a pandering parent, we've just learnt what our boys need us to do and do that).
He sounds so similar to my boys that I'm going to suggest you look up PDA (pathological demand avoidance), but it may be way off the mark. If it is though, you'll be better able to help him knowing what it is and having a few strategies up your sleeve.