how can I get phone numbers of type "inventory" via API?

I have some numbers that employees are migrating and when I search "all phone numbers" in the GUI, I see the number and it says the type is "inventory". when I use the API to get all company numbers, I don't see this number in the list. people have been doing the transferred numbers manually so far, and the automation we made has done the new numbers, but they now want me to process spreadsheets full of transferred numbers via automation. but I can't seem to find these numbers via the API, even though I see them just fine in the GUI. example number I'm speaking of (will redact some, but should be enough to find if you search our account.) 914-***-3592

also, if this turns out to be a thing we can fix, how would I use the api to assign the number to a new user? thanks ahead of time