Mobile DDR-SDRAM for Cyclone IV E

In a DDR/DDR2 controller, I guess that it is only necessary to train the phase offset once as this offset will be quite stable during operation. I guess this is what the ALTMEMPHY is doing during calibration.

But in a mobile DDR controller, this phase offset will change (quite a lot) with the temperature and voltage changes. Then I guess the only way to implement a mobile DDR phy is to have an external temperature sensor and dynamically adjust the phase offset?

Is my understanding correct? Do you know how the voltage and temperature compensation works?

thanks a lot for your help,