In the Instant Pot, combine the broth, shrimp, mushrooms and their liquid, half the coconut milk, the ginger, chiles (if using), 1 tablespoon of the fish sauce, the lemongrass, honey, and salt.
Secure the lid on the pot. Close the pressure-release valve. Select MANUAL or PRESSURE COOK and set the pot at LOW pressure for 1 minute. At the end of the cooking time, quick release the pressure.
Stir in the remaining 1 tablespoon fish sauce, remaining coconut milk, the lime zest, and lime juice.
Divide the soup among four serving bowls. Garnish with cilantro and serve with lime wedges alongside for squeezing.
Notes
NOTE: If you are eating Paleo, be sure to use a Paleo-compliant fish sauce.