A problem you will meet is that Android USB expects to a device and not a USB host.
The USB sockets on a PC/laptop are USB hosts and a USB memory stick or a USB serial port are USB devices. The USB host controls the USB device connected to it. When you connect an Android USB socket to your PC, Android acts as a device and the PC controls it. This lets your Android phone appear as a memory stick or maybe a modem to the PC.
To make the Android phone/tablet control something connected to its USB socket requires the Android unit support USB OTG. This is a method where you can switch the device to be a host. Not all Android devices can do this, some need special software or drivers. So you will need to solve this before you can go further.
You could consider making a simple VOX circuit and use the audio output of the Android unit. Playback tones into the VOX and use it to key the 817.