You can check Leeson formula for phase noise or you can read about the linear time variant theory of phase noise published by Thomas Lee and Ali Hajimiri. Otherwise, you can better the phase noise increasing the Q of your resonant LC circuit, increasing the power dissipation or adjusting the size of your transistors to reduce thermal noise as you did. Maybe it is not a great practice, but you can use the parasitic capacitance of the inductors to tune the frequency of oscillation without the use of capacitors, in order to reduce thermal noise and increasing the Qloaded. Hope it will help