So a little context, 
My fathers health has been declining since last year. Last June we moved everything over into a trust and got his will in order, and set up a full power of attorney for me. We put me as a co trustee so I can add things too it and manage it should the need arise. I took full control of his finances and accounts. In September he had a stroke and this exacerbated things with his health even more so. 
He is currently bed bound un able to walk but still has his mind and wits about him, even though he’s a little slower. 

We always had a family plan and he paid for my grandmas phone bill also, but I always paid him for my portion. Through the years he’s given me several small loans for things, and we had a book to keep track of it. I always paid it down and kept up to date with it. Closer to me taking over his finances and basically entire life, he wasn’t tracking things as much or not really worried about me paying him right away or anything. 

I switched the phone account into my name so I could make necessary changes but kept the bill to his account. Since taking over I haven’t paid it back in several months, but keep diligent track of all other transactions. 

I set him up on state disability, social security, take care of all his insurance issues, found him an assisted living place, and am currently getting his house ready to rent (insane amount of work) so he has more income coming in when disability runs out. I brought my roommates over to help clean out his house and took them out to dinner and paid with his card to say thanks.

Here’s the AITA part. I’m doing all I can for my dad, and have his best interests in mind, but I also don’t want to take advantage of the situation. He’s absolutely fine on money and did a great job setting himself up for retirement, but I’m also not trying to feel entitled because it’s his money, not mine. I asked my mom about it and she said I shouldn’t worry cause I’ve already saved him a ton of money anyway and it’s a “cost of doing business” type of thing. But I’m not sure if it’s a bias with me being her kid. 

Added info, mom and dad are separated but still good friends, also am an only child.

TLDR: Haven’t paid back my dad for phone bill, but have complete POA and am helping him out with his entire life.

Edit: talked with him about it. Go figure, the simplest conclusion didn’t cross my mind.
He said not to worry about it and to keep my conscience guilt free.