I have an unknown app on my phone. I’m concerned it is a bug or malware

If it is possible to take a screen shot and post it, it would help.

In the meantime, try the following in order: (Note: If any step resolves the issue, STOP, do not go on to the next step.)

• Restart your iOS device: To restart your (perform a soft reset) iOS device, press and hold the sleep/wake button while pressing and holding the Home button. When you see the Apple logo, release both buttons. (Note: This will NOT delete any data or apps, nor change any of its settings.)
• Perform a "Reset All Settings" reset: Settings > General > Reset > Reset All Settings

Unless you jailbroke your device, it is not malware. Are you referring to the Voice Memos app?

Force touch on that app until the "X" symbol appears on its upper left corner and delete the app.

If the issue persists, it would be useful if you can post an image of the "light gray app that has lines in it".