They don't need to backdoor the phone, the backups are encrypted to Apple. They divulged user data to the US at least 30,000 times without a warrant/probable cause in 2019 per their own transparency report.
The handset security is mostly irrelevant now that we have cloud-based software encryption backdoors in the form of non-e2e "unencrypted" backups.
Apple doesn't say anything about warrants in their report, AFAICT.
This is false. Like any other computer, they can be configured with more secure or less/in-secure software.