Foam rolling your calves and lower legs without active mobility is useless. So once the soft-tissues are addressed you need to mobilize these tissues through an extended range of motion with bi-phasic stretching.
Since only the gastrocnemius crosses both the knee and the ankle joints (making it a dual joint muscle) as opposed to the single joint soleus and deep flexor group, you'll use two different setups to achieve a targeted stretch through all three regions.
First, using an elevated surface or step, load the bodyweight onto one leg, and with a straight knee drive the body forward and heel down to move into dorsiflexion.
When reaching end range, oscillate on and off with a tiny perturbation for 30-45 seconds.
After the oscillations, hold the end range dorsiflexion position for 1-2 minutes with a static hold. The oscillations plus static end range hold is what constitutes a bi-phasic stretch.
In order to place the larger and more powerful gastrocs on slack, you'll target the deep flexor group and soleus in the same type of setup, but only with a slight knee bend, while the toes and ankle moves into dorsiflexion. Again, use the bi-phasic stretch with the same time parameters and oscillations, just keeping the knee bent throughout the duration of the stretch.
