Ever since DS (10) got his mobile phone last year, there is a constant battle about him wanting to use it all the time.
He uses it to play games and chat to his pals whilst doing it, and also to contact me and his dad.
He plays the 'pokemon go' game so every walk, trip or even shopping includes DS being on the phone for majority of the time.
School runs are a disaster and a constant argument where I ask him milion times to put his phone down and eat breakfast or brush his teeth. He keeps saying 'I'm finishing now' and does that for 30 mins 
Now. Every time I try to limit the screen time and take a phone off him after 1-2hrs he screams and shouts that he hates me, he hates being at mine and loves being at dad's where screen time is unlimited and he is allowed to play games such as call of duty for hours.
Last night he threw his bike and coffee table on the floor once I took the phone off him after 2hrs. This morning he replied that I've to shut up when I said he needs to put the phone down and get ready to school otherwise he is going to be late.
There is an ongoing court case for child residence. At the moment DS is at his dad for majority of the time and I'm trying to get a full custody. I fear the situation with screen time is not going to help and DS asked by the court will say he prefers to stay at his dad's for this reason.
AIBU not to know how to handle this? What is reasonable at this age, how do you handle this with your DCs?