Use the excellent Ecobee Suite linked below. Set up your ST automations to change modes for home/away based on geopresence (phones or other). Set up helpers in the Ecobee Suite app which change the thermostat mode to follow the ST mode. Keep the temperatures as established in your Ecobee profiles rather than controlling directly with ST.
If WebCore is your thing, the app exposes the controls to those automations as well, but you don’t need to learn that if you don’t want to.