Personal hotspot can't be detected on Iphone 6 iOS 9.3.5
for an iOS hotspot to work wirelessly you need to make sure you have the personal hotspot screen (this is the screen that displays the password to your hotspot) up whilst trying to connect and that the wifi on your iPhone is on otherwise your network will be undiscoverable.
Ubuntu should have no issue connecting to a personal hotspot over USB so that may be easier, however that might have changed since I last used Ubuntu.
Hope this helps!