Email On iPad & iPhone not syncing

I have an iPad and recently got a new iPhone 11. Both devices receive emails, but if I delete an email on one device, it doesn’t delete it on the other. I‘ve read some similar questions/answers in here, and tried the suggestions. The only thing I can find is that in Settings on my iPhone, the Incoming Mail Server “Host Name“ is imap.cox.net, while on my iPad it is pop.cox.net. Is this the reason they’re not syncing? If so, which one do I change? If this is not the reason, can you suggest something for me to try?

Thank you in advance!