FWIW, there is an option to do that without even touching the phone:
"Hey Siri, resume schedule"
https://www.ecobee.com/faq/what-voice-commands-can-i-use-to-control-my-homekit-enabled-ecobee3/
Ah, that's good to know. Still the fact that a temperature change done through HomeKit causes the thermostat to behave differently that a similar temperature change through the the native app or the actual thermostat itself.