"skip phones in use" is exactly that...if the phone isn't in use, it'll go to the phone. I can verify that checking "skip phones in use" doesn't solve the issue. The page still went to my headset.

Using CUCM 12.5 & InformaCast Advanced 14.15

While this is an old post and marked "solved" the solution doesn't actually address the issue. 

Many of our users have a headset plugged into the headset port of 8811 and 8851 phones.  The headset is wireless from the base to the earpiece and it's not a Cisco branded headset.  If the last call was on the headset, the multicast alert to the phone displays the message but plays out over the headset, which is inactive, seated on the base.  If the last call was on the handset, the message is displayed on the phone and the message plays out over the headset.

We need to make sure if the phone is inactive, the message plays out over the speaker.  Using the setting to skip active phones does not solve this issue as the phone is in the idle state. Is there a solution to this yet that will force the announcement to go out over the speaker?  This would be regardless of the active/inactive listening device on the phone.

We're on CUCM 12.5 and Informacast Fusion 14.20.2.