Phone not ringing

[#1]

I have had 2 missed calls today that I know of when my phone didn't ring, one a spam call from BT I think on 08003289393 and another from a recruitment agency I applied to.
I did the ring back test and it failed to ring with everything connected as normal.  Then tried with just my phone in the master socket and no filter, that worked.  Then with filter and my router and it worked then.
Possible sign of a dying filter or phone?

[#2]

Quite possibly either; or just a knock or bump that pulled the cable out of alignment? I wouldn't worry too much unless it re-occurs then consider replacing items, cheapest first, until the problem goes away.

[#3]

Possibly only one missed call, as 08003289393 is a generic BT CLI presented when the ringback test facility is used.