Entering data in the field will not work until the field is exited, committed, etc.
Let's assume you have your trigger set to work when the user hits the tab key or even commits the record.
On the popup keyboard there is a down triangle to close the keyboard and a next button to move to the next field that works somewhat like the tab key although I haven't studied it in debth.
The problem is that you and your users are used to tabbing and don't think about it but there is no tab key on the ios keyboard (marked TAB). Try tapping the button Next to see if that will activate your triggers.
Also, you can arrange the tab order of the fields and bypass the need for triggers. This will bring the next field on the layout into focus.
Consider designing layouts just for IOS and not trying to use one layout for everything.
My layout is designed for IOS, thru scripting the user is directed to the appropriate layout depending on the OS. I actually found the solution to my problem after posting this issue. I added (scroll to Object) to each script step and it works the way I need it to now. This extra step was not needed on PC or Mac but adding it didn't effect the way it works on PC or Mac. It's always the simple things that throw me off . Too much over thinking I guess.
Last night I solved a nagging problem with popup menus on Go and here's a link to the post: http://gofm.biz/2012/09/17/go-to-field-filemaker-go/
Go To Field with no field pointer was used as Commit Record long before Commit Record was finally added.
In a popup menu trigger, ending it with Go to Field eliminates moving to another whatever and it solved the nagging problem I had.
This will probably solve a lot of issues for others.
When developing for multiple platforms, a tool to use is to determine the platform: iPhone, iPad, etc. and use an If or something a bit more advanced to determine the layout to go to. Briefly:
If platform is iPhone
ELSE IF platform is iPad