Landline & Livebox prob

We have a simple landline phone (Philips D450) and orange livebox, the phone has started ringing a couple of times for incoming calls, then either cuts caller off or stops ringing although they are still on line. For each call received it now shows callers ID then a second entry of ‘unknown number’, Would you think its more likely a problem with the phone or livebox?

Suggest taking the Philips out of the equation first and substituting it with a very basic no frills standard land line phone - plug it to the T connector on the livebox and see if it works. Either borrow one or buy from the local supermarket (not in the least bit expensive).
If it work without problem, it could point to the Philips.
If there is still a problem, at least you have eliminated one issue from the equation and can proceed to the next one.
Don’t know your set up so can’t comment but if you have the Livebox connected to the line via a filter, try replacing that - again, not expensive from the local supermarket.
A 'dead-ringer for this type of problem is if it suddenly occurred after the recent thunder storms. They do tend to hit filters quite frequently.
Just a matter of trial,error and patience to eliminate the possibilities before calling on Orange to replace the Livebox as a last resort.

Are you getting any incoming calls? If not get someone to phone you so you can see if all is well or not. The strange calls could just be market research seeing which numbers get answered at a particular time of day.