You are doing really well OP. This is a v complex and enmeshed emotional situation where normal rules don’t apply.
100% keep his phone - and don’t get cross when he doesn’t respond - because it’s v v likely that she is screening, monitoring, censoring his phone and his interactions with you.
If the driving lessons and lifts to sports provide any one to one contact time with him seize it - little and often, simple opportunities where he can rebuild his trust and speak to you safely. Also you need him to be engaged in anything and everything where he gets to be away from her crazy home and immersed in normality.
Is the “you don’t love me comment” a new thing with him? I suspect that she is drip feeding this in his ear.
I expect he is very confused, ashamed and vulnerable.
Just keep being consistent, calm, light, available - keep that rope dropped because that previous tug of war tension is the energy in this RS. She needs this drama to triangulate the RS - once you step back then the valency isn’t there and it falls apart.
As others have said - let him know that he is loved and welcome home - that he can be collected at any time. Focus on him - don’t refer to the RS.