The two most practical solutions:
1) Turn your phone off
2) Settings > Voice > “Ok Google” Detection > From LOCK screen OFF
But if you do want to leave it on, then I think its what you would hold for an automatic light on the front of your neighbor’s house – you might cause it but you have no intention of it and are not trying to make the object do anything.
We had a situation with an automatic door to get to the Succah in a Nursing Home. They would lock the door on ‘open’ but the sensor was still on and clicked when we walked through. Now we get the power to it turned off beforehand, but according to some its still OK if it hadn’t been turned off (obviously turned off is better) and according to others its not.
So, like most Halachos of this nature its a Machlokes and I agree that you should speak to your local orthodox Rabbi.