Why is this Type I compensator phase not 270 degrees?
The op-amp you have used has a DC open-loop gain of only about 54 dB and I expect the capacitor C1 doesn't start to "eat into" the open loop gain until some frequency that is higher than about 10 Hz.

An integrator is only as good as the open-loop gain (at low frequencies).



I will also point out that in the circuit you show (with R2 connected to ground) R2 has no effect on the frequency response of the circuit and that your equation for the gain and integrator time constant does not involve R2. The -input of the op-amp is a virtual earth for AC signals.