>IP address?
It's like a home address, but most of the time dynamic, so it's like moving to a different address every day or so.
>new iPhone, new IP
With shitphones, you get dynamic IP addresses most of the time, so you don't have to buy a new eyePhone to get a new address.
Btw. you can easily check your external IP address by going
https://whatismyipaddress.com/
You can check every day or so and see if it changes or not.
Your home IP address may be fixed.
>new ISP
yes, that will definitely get you a new IP address in any case, but it doesn't really make sense in your case.
>spying
If your phone is hacked, consider it compromised (it is compromised regardless) and factory reset it or sell it.
You need a password for e-mail. If your phone got hacked, your passwords may be compromised.
So you would need to:
>change hardware
>change all passwords
With the right password, someone can read your e-mail without your hardware. That's of course depending what kind of e-mail access it is.