How to manage 50+ Twitter Accounts from same device without getting banned?

Jarvee is your solution.

Do we know the max accounts that can be associated with single phone number? I looked on their help files but didn't see a number given.

What do you want to do with your accounts? If you want to automatically tweet content in a set-it-and-forget-it way, I've been using a new site I found that's been working pretty well. DM me if you're interested. I tried doing the whole auto-follow thing but you get shadow banned fast.