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Survivors often come to me with concerns that their iPhone has been compromised and tell them that they have purchased a new one to mitigate this. Here is why that is usually not an effective solution:
Fashions in iPhone malware come and go, depending on iOS vulnerabilities, but most iPhone malware does not get directly installed on your phone. It works by scraping your iCloud backups.
As long as your iCloud account is compromised, the attacker will keep on getting a regular snapshot of everything that is happening on your phone even if you get a new phone.
Some better mitigations include: changing your iCloud password to lock the attacker out of your account, and/or turning off iCloud backups and backing up your iPhone locally to a computer you own and trust.
This guide to locking an abuser out of your Apple devices is really great and lays it out with great clarity:
