The short answer is, it depends on how your wife feels about you at the present time.
Because:
It is wrong to sign someone else's name to anything, where the person to whom the signature is presented is not aware that the signor is not the person whose name he/she signs. In other words, it's wrong because it's a lie.
But for it to become a criminal offense (fraud) it would take a complaint laid with the bank or directly with the police.
Who would complain? If it's just between you and your wife, and she gave you her consent, she's not likely to report it as a fraud, is she?
It was probably just one of those awkward things, she's out of town, an urgent bill is presented to you, phone service will be cut off unless paid immediately, but your account is tapped out, etc, etc.
So she just says, "Sure, just take a check out of my checkbook and sign it. They never check signatures."
She's right. Unless there's a complaint.
But who would complain? Certainly not the phone company. It's in their interest that the check is good. Certainly not her, since she wants the phone to continue to be in service as much as you do.
So you're home free.
BUT If you wrote a check for a gambling debt you owed, or payable to yourself, or your girlfriend, on her account, and she later challenged it, you would not look very good claiming she verbally authorized you to sign, if she denied it.
And even if she did authorize it but later denid it. It would not look good. For you. Others
(such as the judge) might doubt your sincerity that she verbally approved.

So. She knows this. That is why I say that it depends on how your wife feels about you at the present time.
Also that is why it is not a good idea to do it.