I gave DD my old iphone 6 when we went to DLP when she was 11, so that she could take decent photos, she is 13 now and I only just bought her a refurbished iphone 6 for £95 as the other had a bad battery and smashed screen. No way was I spending more money on something newer .
I won't be buying her anything else for a long time. It is a smart phone and it does everything that she needs a phone to do. She loves it.
Your son does need to understand that we dont always get what we want in life, and that his time will come, and when he is old enough with his own money, he can buy what he wants, or agree a deal that he can have a newer one for next birthday/Christmas, and agree a model/price in advance.
I very much doubt that his counsellor agreed with him that you should get him a new phone. I would say he is fixating on this because there is a problem in another area of his life.
If you do get him a sim, Smarty have some good deals, or Giffgaff is another one.
I also agree with PP, it's that phone or no phone and if he goes on about how bad it is, it is taken away from him. and I agree with another PP, rinse and repeat. I tell DD, we have discussed this, you have my reply, it's not going to change.