Unfortunately no easy way about it :(

You can sorta increase keyboard size by going into accessibility settings > display to increase text size as a whole.

As for additional number line on iPhones, not possible without third party keyboard afaik, but there’s a couple tricks (link to reddit comment) to speed up typing numbers. iPad has the number line in their keyboard.

I’m just used to not having these features in exchange for generally much better integration of autofill passwords etc. I have an android tablet to compare with & it’s a pain to have to switch over to a dedicated keyboard to access my passwords & back because swiftkey borks it most of the time (I use keepass as a password manager). The keyboard also auto-detects those pesky SMS OTPs, which is a small convenience but surprisingly satisfying to not have to flip apps/squint at the number in my notifs to slowly input it. Pros & cons I guess.