How can I make Text be just Text?

Settings, messages, iMessage needs to be on.

Then underneath in Send & Receive, make sure only your main phone number is checked/ticked. Not your iCloud email address.

iPhone will always use data to send "text" messages to other iPhone users.

Ask Siri to send iMessage to.....

It seems you are not understanding how iMessage works, and this stems from the confusion of "text" and "text message". An analogy is the use of "call" when you really mean "telephone". You personally may always use a telephone, and never cup your hands in a megaphone shape and raise your voice, to call someone, but many do.

When you are in iMessage, Contact entries as you search for them will show up in either blue or green regardless of whether the identifier is a phone number or an email address. Blue entries will be handled by the iMessage protocol and green entries will be handed off to your cellular service provider's MMS service. MMS messages will be handled according to the rules your cellular service provider sets.

Blue targets are handled by iMessage. In this case, Apple simply facilitates a direct connection between you and your target(s), using the telephone number and email address labels as identifiers but not as delivery methods. There is no Apple messaging server engaged in this process, so messages that cannot be delivered in real time fail. This is why you may from time to time see that a target you know to be an Apple device lights up green. If the device(s) is/are off line for any reason, that target will light up green and iMessage will not work. In any case, iMessage will never hand a "blue" message off to a cellular provider or email provider for processing.

I gave you a solution that worked for me, just use "iMessage" instead of "Text" if you want Siri to comprehend.

The word text has many meanings as you and others explained, the word iMessage does not

If you have a disability that prevents you sending an iMessage the normal way please explain.

Hey, Siri (pause) send iMessage to Joe Smith Mobile

This assumes you used "mobile" as the phone number type.

The word “text” has multiple meanings. I think it’s unreasonable to expect Siri to read your mind to determine what type of text you are asking about.