If you want to actually embed it within the PowerPoint slide itself, I'm afraid there is no easy way to do this.
The only video objects that PowerPoint can natively embed are Windows Media Player objects. Hence, the only type of live stream PowerPoint can embed is a Windows Media Encoder Broadcast. Unfortunately, no app exists that streams your phone screen directly into a Windows Media Encoder broadcast.
The best solution would be to just use a screen copying application like scrpy, which is relatively simple to do.
Of course, if you really insist on it being embedded within PowerPoint, it is technically possible (I've had to set this up for a conference) — it's just really complicated:
- Stream your phone screen to YouTube via the YouTube app.
- On a separate device equipped with a video capture card that has a live USB or HDMI output, pull this live stream up in fullscreen.
- On a third device, connected to the same LAN as your presentation device, create a broadcast in Windows Media Encoder using the capture card output.
- On your presentation device, in PowerPoint, insert a Windows Media Player object and select "Properties". Enter the link-local IP address of the broadcasting device and the port specified in step 3.
- Play the slide show, go to the slide with the embedded object and press "play". You should receive the live video stream right within the slide.
Please note that this approach can suffer from issues with latency and reliability, and is quite difficult to troubleshoot. Broadcasting via LAN will often not work depending on how that particular LAN is set up (this is especially likely with corporate or academic networks). A tunneling tool like Hamachi can be a viable workaround; if that fails too you would have to broadcast via the Internet, further increasing your latency.
Ultimately, I would highly advise against this approach and just use scrcpy instead. The visual appeal of having the stream embedded in your presentation really isn't worth all the effort.