Use an active PS/2 -> USB adapter as USB-Serial Bridge
Basic USB is an asymmetric connection: a master connects to a slave. You can't connect two masters or two slaves (you can if you rewire cables, but it won't work).

The USB cable for your phone connects a master (the PC) to a slave (your phone). The PS2-USB converter is probably a slave that connects to your PC (the master). (Your PS2-USB converter could be less than a slave, if it relies on keyboard to do part of the job.)

Hence you can't (successfully) connect your PS2-USB slave to your phone slave.