iCloud Backup

Hi! I have been trying to do iCloud Backup but my phone always remains at “Estimating Time Remaining” and it would take hours of NO PROGRESS. I have my original storage at 256GB (used: 245GB) and I have upgraded my iCloud storage at 2TB (used: 350GB . I don’t understand why my iCloud backup seem to not make any progress every time I attempt to back it up. I’ve done it on locked, connected to power and on WiFi— still no progress. What should I do? I hope someone can help me. Thank you in advance!!