Phone icon is missing from dock

Search your screens and your folders, it may have been inadvertently moved to a different screen or inside a folder.

You could also try going to Settings->General->Reset->Reset Home Screen Layout.

This should put everything back into the default order for preinstalled Apps, and alphabetical order for everything else. All folders will be destroyed though.

The Phone icon should return to the dock. as that's its default location.

You can't delete it. You must have moved it.

If you can't locate it to move it back: Settings>General>Resets>Reset Home Page Layout.