Any way to sync/connect vivosmart HR with a phone based GPS app?

Not in the sense of using Garmin Connect as a data integration platform, and somehow enriching the activity records produced by the vívosmart‑HR with GPS data (from either the mobile device's GPS capability or some other GPS feed).

If you just want to use the vívosmart‑HR as a heart rate sensor to provide a live feed to an activity tracking app, and you have a mobile handset that is compatible with ANT+, then something like the Wahoo Fitness app can be used to track your HR-monitored workouts.

I purposely didn't get the HR+ because I'll always have my phone with me and it already has a perfectly good GPS built in.

OK, and? Interoperability is not something you can take for granted, and acquiring a minimal set of hardware capabilities (to contain your spending and/or clutter) but getting overall capability that is significantly greater than the sum of the separate devices, is a lovely consumer ideal but not automatically supported by manufacturers. It's far better to buy self-contained units/packages of technology, even if that means having to spend more in total on overlapping capabilities and features, if achieving the functional outcome is more important than budgetary control.