US: From what I understand, in the US cellphones work differently than they do in other places in the world. Here many (most) people sign up for a cell phone contract with a company that says how much data, minutes of service, texts, etc. you can use and how much everything will cost/month. The contracts last 2-3 years. And the company you get cell service with oftentimes gives you a phone "for free." The contracts also say how frequently you can upgrade your phone (without paying a lot extra). If you want a new cellphone, but your contract doesn't let you have a new phone until 2021 - you're "stuck with your phone."

If your question is - What does "I'm stuck with my cell phone." mean. Then it can either mean "I have a mobile phone, which I cannot change right now" - this might be because in order to change their phone, it'll cost a lot of money, which might not be an option. It can also mean "I have a mobile phone, and I'm having trouble using it" - "stuck" can also mean "having difficulty" - so you could say "I'm stuck on this maths problem" So without any other context it could mean "I have a mobile phone which I cannot change right now" or "I have a mobile phone which I am difficulty using right now".

Thank you!

"I'm stuck with xxx " quite often means "I'd like to replace xxx, but for some reason I cannot." This might be because of a long contract, in the case of a cell phone. https://www.ldoceonline.com/dictionary/be-stuck-with-something