If your phone or tablet is connected to Spire Studio, monitoring and playback can be heard only via the headphone outputs on the Spire Studio hardware. To adjust the output level, start by pressing the "Volume" button on top of your Spire Studio. After the Volume button lights up, you'll be able to drag your finger along the LED ring around the edge of the top of the Spire Studio. Dragging clockwise will turn the volume UP, while dragging counterclockwise will turn it DOWN.
Please note, Spire Studio comes out of the box with this level set very low, so it is likely that you will have to increase it in order to hear your project at an adequate volume.