Timers for on/off delay

Setup, Configuration and Use Beginners
2

RULE FILE for a timer that is triggered/retriggered when a specific item receives an update.
This works for all the use cases you describe above:

In this case “var Integer pantry_timeout = 1” defines a timer with a duration of 1 minute.
Each time " MotionSensor_Pantry_Motion" is updated the timer is triggered/retriggered for the duration of “var Integer pantry_timeout = 1”.

For presence purposes like you described you would replace " MotionSensor_Pantry_Motion" for a switch item that represents your phone.

But please look around on the forum a bit, there are several better ways for presence detections using phone-openhab. (expire binding, Unifi binding, dd-wrt trick)

var Timer pantry_timer = null
var Integer pantry_timeout = 1

rule "Pantry light motion"
when
	Item MotionSensor_Pantry_Motion received update
then    
	if (MotionSensor_Pantry_Motion.state == ON && Night.state == ON) {   
  	  if (pantry_timer != null) 
    {            
        pantry_timer.reschedule(now.plusMinutes(pantry_timeout))
        logInfo("Lights","Pantry light timer rescheduled for " + pantry_timeout + " minutes")
    }
    else
    {            
        sendCommand(Switch_Pantry_1, ON)
        logInfo("Lights","Pantry light timer created for " + pantry_timeout + " minutes")
        RulePantryLightMotionTS.postUpdate( new DateTimeType() )
        pantry_timer = createTimer(now.plusMinutes(pantry_timeout)) 
        [|        
            if (MotionSensor_Pantry_Motion.state ==  ON)   
            {
                pantry_timer.reschedule(now.plusMinutes(pantry_timeout))
                logInfo("Lights","Pantry timer triggered, but rescheduled again for " + pantry_timeout + " minutes")                    
            } 
            else 
            {            
            logInfo("Lights","Pantry light timer expired")
                sendCommand(Switch_Pantry_1,OFF)
                pantry_timer = null
            }
        ]
    }
}
end