How do I send and received texts on my Windows PC without an android phone?

here some methods described :  How to send (and receive) messages on a laptop or PC - TechEngage 

You could use WhatsApp but you would still need a mobile phone of some kind to authenticate

he has an iphone...

Your Phone does not have the option to select the OS and appears to work only with Android phones.

Which cellular service provider you are using?

It might be possible that some cellular service providers will allow you to send and receive text messages via their web portal.

Verizon.   I believe I need to know the service provider of the person I an trying to text.   If I do, then I can send the text via email.   Unfortunately, I do not always know the provider used by the recipient and they sometimes switch providers anyway.

I tried the Verizon portal.   It refused to accept the verification code, so I just gave up.   I also tried the Dell Mobile Connect app.    It works sometimes, but keeps losing Bluetooth pairing with the phone.

How is your office gets phone service? Cloud based 8x8 or ringcentral, etc. include virtual phone option on a mobile/computer

Check with your software vendor, presumably this is where you need this to see which vendor they support to facilitate the Sending and receiving of messages.

Vonage offers such a service, API...

I tried the Verizon portal.   It refused to accept the verification code
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​You might need to temporarily turn off iMessage as it seems that the verification code you received has been expired due to a delay in receiving the same via iMessage.

1. On your iPhone, go to Settings.
2. Tap Messages.
3. Set iMessage to Off

Jackie, the person might be trying to add features to their practice to facilitate PT communication,notification.
The sending sms, is not as complicated as being in a position to receive the within the same process, app.

The iPhone, might be a means.
Might the need deal with appointment reminders and confirmation, cancelation..