iPhone 17pro not backing up

I have been trying to backup my new iPhone 17pro for 2 weeks. I've done every single thing Apple says to do correctly, and decided to try again last night. This morning it said 18 hours remaining for backup. Then 5 hours later, I looked and now it says 1 day. Why is it taking so long?? I have decent wifi. No apps running in the background. It's plugged in to power. It is running the most current iOS. My ipad is backing itself up every few days with no problems at all. Why the new phone??

thank you.