Hi Both,
Thanks for the quick replies. I sure am grateful for your contributions!
Really don't know how I set this flag as I didn't do it manually and didn't dial the feature code. I checked Phone-Related Information > Flags > Handsfree and noticed a few people were in there, including a colleague I share a room with. I'm 100% sure I have never heard her phone auto answer. She would be quick to bring it up if it was happening. Anyway, I left those people there and checked Ring Intercom Always, which included switchboard, so added all the other internal staff too.
My phone is back working normally now.
Thanks again. Very much appreciated.