GuiScales is an application that displays scales/modes on a fully scrollable virtual guitar fretboard. (not tested on latest generation iPhones)
Just select the key and the scale.
At the bottom of the screen is the notes in the scale, which are selectable. Once selected the note is highlighted.
Highlighting 2 notes will help with Intervals, 3 or more notes will help show you chord notes. (relative to the root note/scale). It's not perfect in that it would have been nice to change the root note to one of the other notes in the scale. Maybe a future update.
Notes are displayable as Notes, Simplified and Numbers. Notes shows notes as musically accurate* named notes, Simplified naming shows notes names in a simplified format such E♯ being shown as F, Numbers shows the notes with a numeric naming e.g b3 5 etc
Selectable scales: Major (Ionian), Dorian, Phrygian, Lydian, Mixolydian, Minor (Aeolian), Locrian, Harmonic Minor, Melodic Minor, Minor Pentatonic, Major Pentatonic, Blues.
*every effort has been made to ensure accuracy