Outlook 365/current version iOS/Win10.0.19...

Intent: Send a group email from the iPhone using iOS native email client.

What I've done:
1. Created 'Test' group in desktop OL contacts containing 3 contacts/emails
2. Open contacts on the phone
3. Click Groups (default the following are all checked: All Exchange, Contacts, Search results - Exchange Global Address List is unchecked, checking not good result - left unchecked)
4. Click Done
5. Type 'Test' in search box
6. Test does not appear in either the 'Top Name Matches' or 'Other Results'

I give up.

Mark