Question is if your board supports AVRCP controller BT profile?
If it does you "only" need to connect against your phones AVRCP target BT profile. When you have a AVRCP BT connection there is specified commands how to pause and skip songs.
This is how the "plug and play" headset does.
Read more about Bluetooth profiles. http://en.wikipedia.org/wiki/Bluetooth_profile
Looking at your code you have set up a serial link towards a phone. This link uses SPP profile and you will only be able to send raw data over that link. If this is the only profile that your BT stack on your Arduino Uno board have you will be forced to create an application on the phone side to be able to read the raw data and do something with it e.g. pause music.
Hope this cleared things little for you.