Can I use my Android phone as a TV remote

Make an IR REMOTE WITH ANY SMARTPHONE PHONE

App link

https://play.google.com/store/apps/details?id=com.tiqiaa.remote

Iphone app

https://itunes.apple.com/us/app/zaza-remote-universal-remote-control/id717545062?mt=8

how this works 

Audio port can send any kind of signal you need. It can be either digital I/O signal or basic analog signal. It's all about application you will use to generate signals and a way you will light up IR LED. You may need some extra circuitry for this since audio output has very low power, so you may use transistors as amplifier.

Circuit I draw can control two devices in same time without need for multiplexing (one LED, multiple devices).

You should use application which will generate square wave digital signal.

So, either HIGH (1) or LOW (0). That way transistors will light up IR LEDs on HIGH.

step 2 you can try this (home work )

You can use an NODEMCU (ESP8266) & connect it to your local WiFi network at home. Then place it in a nice box in the drawing room, like this one which I drew.

Have it run an example mDNS sketch with the IR libraries from github & make a simple android app to send 2/4 commands over http to it. Its most likely going to have a fixed IP(in hotspot mode) or using the mDNS you can connect to ex. esp8266.local.