it's bcoz phone app is buggy. It makes min-cpu-freq dropping to 125 Mhz when using the phone app. Default min-cpu-freq is 250. U can change this by installing titan-power-kernel and pick one of the default power profile ( kernel-config load ideal ) and such avoid 125 Mhz cpu-freq. to install titan-power-kernel go to program manager and install enhanced kernel for power user and enhanced kernel for power user ( settings ) and rootsh by pressing the first letters of the program and select them in the touchpanel and type sudo gainroot and kernel-config load ideal and kernel-config default ideal in x-terminal.