Welcome to iMore. There is no altimeter in the compass app the comes with IOS. You will have to find a separate app for that. Such as [URL="https://itunes.apple.com/en/app/digital-altimeter-free/id336650411?mt=8&at=10l3Vy]Digital Altimeter[/URL] which is a free app in the iTunes Store. Hope this info helps.
Since that phone comes with a BMP 280 Bosch barometric sensor you would figure the app would have an altimeter. There's quite a few altimeter apps on iTunes you can get though. The one named Barometer & Alitmeter for iPhone/iPad has really good reviews.