Intermittent connection with iPhone

[iPhone]

I’ve been experiencing intermittent connection on my iPhone 7. It’s been ongoing for a couple of months but these last few weeks it’s constant. 
It’s been checked and was told it’s because device is old, but that is happening also for my iPhone 13. 
what I don’t understand is ‘do I need to change phone to get WiFi connection?’

I believe it’s something to do with the router but they say it’s not. Yet it is quite an old Talktalk router. 
All lights on router are green and flashing yet no devices connect. 
Please can anybody help? Thanks

[Gliwmaeden2]

Which specific router have you got, @iPhone?

There have been occasions where iphones have problems connecting to the wifi.

Staff will be back on here after the weekend. Make sure that you have completed your community forum profile details for Talktalk staff to identify your account, @iPhone.

Go via your avatar; settings; add your Talktalk phone number or account number in Personal Information. SAVE CHANGES.