You'll need an I2S decoder board. I have used both with success: Max98357 I2S 3W Class D Amplifier DAC Module CJMCU-1334 UDA1334A I2S DAC Audio Stereo Decoder I think at one point I also used the ...

Adafruit I2S 3W Class D Amplifier Breakout - MAX98357A This board converts the digital audio data from the ESP8266 I2S controller to analog audio and amplifies the signal to drive a speaker. This ...