Q: how can I reset phone? Keypad will not work

Since the malfunctioning screen is likely due to water damage, not much at least form the phone itself. You can try restoring as new from iTunes on a computer.

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings - Apple Support

Using a computer, go to https://icloud.com/find and erase the phone. Then remove it from your account. If the phone isn't working this will not actually clear it, but it will disable Activation Lock. And, if you have a lock screen passcode no one will be able to access your data, even by disassembling the phone.

Lawrence Finch wrote:

 

Using a computer, go to https://icloud.com/find and erase the phone. Then remove it from your account. If the phone isn't working this will not actually clear it, but it will disable Activation Lock. And, if you have a lock screen passcode no one will be able to access your data, even by disassembling the phone.

DOH!