Backup stuck at Estimating time Remaining

Thank you for providing extra information!

Is there a Mac or Windows computer you can access? It sounds like you may need to backup your iPhone over a wired connection. Please take a look at these articles:

How to back up your iPhone, iPad, and iPod touch with your Mac - Apple Support

How to back up your iPhone, iPad, or iPod touch with iTunes on your PC - Apple Support

I hope this helps!

Hi!

Backing up your iPhone may take a while, especially if you have lots of data to back-up. Please ensure you have a strong Wi-Fi connection, as this will speed up the process. Backing up over a 4G connection, for example, will slow the process down significantly.

Hope this helps!