That looks like it might work, I appreciate it! You need some way to pump both the PS4 game audio and either PC or smartphone audio (depending on what you're using with Discord with) into your headphones, using a mixer of some sort, or your PC if it allows it. They're not wrong in the sense that you can use the smartphone app for console gaming
If your headset volume is too low, you can adjust the volume controls in your PS4 device. To do this, go Settings > Devices > Audio Devices > Volume Controls. Use the slider to increase it to your preferred level. Avoid taking it too high because loud sounds can damage your ears.VNdl0.