airpods won't connect to apple watch when phone is not around

Hi. So I bought my wife an apple watch (series 9) so she could walk the dog and listen to podcasts without having to take her phone with her. When she's in the house it all works fine. As soon as she walks 1 door up the street it all cuts out (airpods disconnect) and she comes back and takes the phone with her. Its like the watch is just controlling the phone to stop / start things.

I can see the airpods connected on the watch, yes the podcasts are downloaded/syncd to the watch.

I managed to get it to work once (ie leave phone inside and walk off still listening) but can't repeat it...

Does anyone have any advice?

thanks....