Using your personal im for work business is a world away from

1 - incidental use of your cellphone for work, even things such as securing work email via 2fa; 2 - using your phone to answer work email via remotely revokable gmail access; 3 - using your personal laptop to answer work email, again via gmail

none of 1-3 mean an employer should get the rights to view my personal email which is also on my phone, or to look inside my phone at all