It is not necessary to carry your iPhone during elliptical workouts.
To credit progress towards your daily Exercise goal, Apple Watch aims to identify activity that equals or exceeds the intensity of a brisk walk. The definition of a brisk walk varies from person to person and depends upon your personal information.
To check that your personal information is accurate - and to update it over time:
- On your iPhone, in the Watch app, go to: My Watch > Health > Edit - tap and adjust items, then tap on Done.
Calibrating your watch can help to improve the accuracy of various estimations (including Exercise credit) made by the Activity app and Workout app. More information and instructions for calibrating your watch are available via the link below.
If you would prefer to record your elliptical workouts as Exercise regardless of their intensity level, track them via the Workout app using Other as the activity type. This will credit one minute of Exercise for each full minute of your workout. Calories will be credited at a rate that is equivalent to a brisk walk or based on data from the heart rate sensor, whichever gives the higher result.
More information:
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support