I can imagine how frustrating it must be to have your text notifications disappear on your phone! At this time, there is no way to adjust the setting, so if your messages are open on your computer, it will recognize the message as read on your phone. I will lift up your suggestions to our leadership team, to see if they can be included in a future update.
If my response answered your question please click the _Correct Answer_ button under my response. This ensures others can benefit from our conversation. Thanks in advance for your help with this!!