external volume not working after water damage

Hello,

Yesterday, I dropped my iPhone 4 in water and got it out really quickly. I left it in rice overnight and fortunately I'm only having one problem with it now:

The problem is that the external volume is not working. I cannot listen to music or videos without the headphones being plugged in. I can, however, hear my phone when it rings/alarm, when I am on speaker, and for incoming and outgoing calls. The volume slider does not appear on the screen when I use my up and down volume buttons unless my headphones are plugged in.

I have already tried cleaning the headphone jack and usb port with keyboard air in a can cleaner.

Any additional ideas to help? Also, if I could narrow down the problem to one specific part, that would be helpful.

Thank you!