Can I use my ip67 rated iPhone in the shower?

Its rated to do so. But keep in mind if anything does happen its not covered under warranty 

WTF would you need to use a telephone in the shower?

if you want to i recommend putting it in a plastic bag. if i dont have time and have to shower i put my phone in a nag even though its water proof

No, you can't. IP67 is rated for submersion in water which is cold. Using it in the shower will not protect it sufficiently as the water is hot which will expand the components of the phone and expose it to water. Do you really need to use your phone in the shower? Can't you leave it alone for 15 minutes?

IP67 can sustain 6 gallons of cumshots too. so yeah you can masturbate in the shower comfortably without worrying too much.

Put down the phone for the whole ten minutes you are in the shower.  Obsessed much?

It's rated to withstand submersion in up to 3ft of water for 30 minutes but that doesn't necessarily mean it's a good idea to use it in the pool or shower. It's still on you if it gets damaged as a result of liquid contact since any kind of damage to the screen or enclosure can compromise the water resistance.

Yes, Put it in a Baggie first.Then seal it.