Trying to apply multiple formula to a cell, works great, but how on earth do i fill down !

Afternoon All.

Hope we are all well in this crazy old world.

I'm hoping that I can be cheeky enough to ask for a bit of help with some excel formula work.
to give you some background, I work in telecoms so therefore any numbers that i refer to are generally telephone numbers in the UK.

I’ve attached my file which wasn't originally set up by me, so its had to be unpicked a little.

The blue/Purple cells appear to be some logic that was put together several years ago to define if a phone number is a Platinum, Gold, Silver, Bronze or standard number.
It works fine for whatever number you type into cell B2, as it automatically puts into cell D2 the Category that the spreadsheet defines the number is. My target out of this piece of work is to have a list down Column B starting with 08444430000 and going up to 08444439999 and against each of those cells, in Column D I am looking for the category that the number would be placed into

sorry if it’s a dumb easy thing, I've pondered and played for hours and just can’t get my head around it.
So anything you can help with would be beyond amazing