The softy~Walter Dad is doing so much harm by being a soft~soaping ninny.
If he makes a 'Punishment'..Like takes phone away or whatever..he should stick to it, and not be a wimp and give it back on some pretext for a 'Quiet life'
He's giving in as it's easy to give in!
No backbone.
I locked DS's phone in a room once as a consequence, and he actually got the wood splitting axe and hit the Victorian panelled door to get to it. {Not a smartphone, even}
I called the police {On advice of a very experienced counsellor who had himself been a tricky teen }.
The police were very good, and to this day I don't know what the copper said, but he was very effective. {Thank you, whoever you were!}
DS was never disruptive at school, though, just a bit 'Flexy' at home, as he too didn't have Dad living with us.
Boundaries work better with some kids than soft soaping and making endless excuses for them.
It isn't easy.