How do I play Netflix on my IPhone but watch it on my Tablet?

I have an HP tablet that I like to hook up to my television and watch movies from via HDMI. I don't have a Wi-Fi plan only data and my wireless hotspot isn't enough data. I want to play Netflix on my IPhone SE then have it play on my Tablet so I can watch it on my TV. Is there something I'm missing on the Netflix app to allow a second screen?

You need to buy an accessory that allows you to plug your phone into a HDMI cable.

It sounds like you are confused.

If you have enough data allowance to watch Netflix on your phone, then enabling its hotspot and watching Netflix on your tablet instead should use the same amount of data.

You never have a Wi-Fi plan. Whether you connect to the Internet over the cellular network or from a land line ISP, all that gives you is an Internet connection. It is of no concern to the cellular or land line service whether you use it over Wi-Fi, Ethernet or USB. The service provider does not know or care how the Internet connection is being used.

Depending on your Netflix contract you might be restricted to using a single device at a time, or allowed to use two (or possibly more) devices simultaneously. Particularly in the first case (one device), you might have to wait some time after turning off one device before you can use Netflix on a different device as Netflix has to time out the idle connection to determine that the first device has detached.

You might investigate using a Chromecast dongle on the TV. Start Netflix on your phone and then transfer it onto the Chromecast. It transfers the movie stream to the dongle. In the case of Netflix, the dongle takes over the session completely from the phone. This also applies to Youtube streams.