Your work tenant blocks the iOS Mail app but still allows Outlook on the Web in Safari on a Mac. On iPhone, Safari can request the desktop version of outlook.office.com — your tenant then serves the same OWA experience and you sign in with your normal work credentials.
Open outlook.office.com in Safari →Tap this on your iPhone in Safari, then follow the steps below.
In Safari → Settings → Websites → Request Desktop Website, add outlook.office.com so it always loads as desktop. Then Share → Add to Home Screen for a Mail-like icon on your springboard.
Not affiliated with Microsoft. Your credentials go directly to Microsoft's login page in Safari — nothing is stored or proxied by this site.