Creating a voice shortcut to navigate between sheets in Numbers

Not using Shortcuts, no.

You might be able to invoke a shortcut via a voice command, but the shortcut doesn't get to see the voice trigger you used, so it wouldn't know what number you quoted. Theoretically if you created 60 distinct shortcuts, one per sheet, with 60 distinct triggers, you might get somewhere, but that's a lot of overhead vs. one shortcut that responds dynamically to the trigger.

Even then, Shortcuts is severely limited in what it can do. Since Shortcuts are designed to be cross-platform, they're pretty much limited to lowest common denominator functions, and 'go to sheet' is not one of the standard commands that Numbers supports via Shortcuts.

It can be done via AppleScript, but getting voice triggers to run an AppleScript is tricky. If you can be happy with some non-voice trigger (such as a menu or command-key action) then it could be done, via something like this (paste into a new Script Editor document and click Run:

tell application "Numbers"
	set currentDoc to front document
	set sheetCount to count sheets of currentDoc
	set promptDialog to display dialog "Enter Sheet Number:" default answer sheetCount buttons {"Cancel", "Go"} default button "Go"
	set targetSheet to (text returned of promptDialog) as number
	if targetSheet ≤ sheetCount then
		set active sheet of currentDoc to sheet targetSheet of currentDoc
	end if
end tell

When run it will prompt you for a sheet number to enter (default being the last sheet so you have some idea of the bounds). Assuming a valid number is entered, it will take you to that sheet number.

This can be saved as a script and launched via Services, or included in an Automator Workflow (as a Quick Action with the Run AppleScript action)