Existing Apple Music synch to family plan

I do not have an Apple Music subscription and my iTunes loaded Apple Music app is taking up too much memory on my iPhone. To get the “optimize storage” feature, my wife added me to her plan via a family plan. But it did not synch up my existing library/account. How do I get it to do this so I can optimize? I don’t want to change any of my existing info as it has all my iTunes purchase info and my entire library (many loaded CDs). Why won’t it just synch the accounts?