I started having the same problem of Appointments getting converted into Meetings after they are edited using Apple's Calendar App on my iPhone. I got worse result when I attempting using Outlook for iPhone - all Appointments look as if they are Meetings
when viewed from Outlook for iPhone. The problem started this week after update of Office 365 Home and update of iOS to Version 11.3.1. Seems that Outlook Team needs to fix Outlook to restore Appointment functionality for both Apple's Calendar App and Outlook
for iPhone.
Thanks MG .... it's not just me then. I agree with all you say as I've done test event entries via PC Office Outlook, iOS app and Outlook app. The 'New Appointment' on PC seems to create a meeting - me as organizer (poss Skype address) and me as attendee
(email account). (The event is lighter in colour than an appointment and has a dotted line around it - does that mean meeting????) Creating through either phone app seems to give an appointment. I wander if deleting and re-installing my outlook.com
account from PC Outlook would solve the conflict?