Hi,
The User Guide doesn't specify how many Bluetooth connections can be 'stored' in the speaker.
Did you try turning off the Bluetooth in your phone before you tried pairing with your tablet? If that doesn't work, then I'm guessing that it can only 'store' the one Bluetooth connection.
If you want to pair with another device, press the Play/Pause button for 3 seconds to disconnect the first device, you will get a tone then you can proceed with the pairing of the next device.
Here is a link to the User Guide which explains it better. See Pairing Your Device box
http://ns323666.ip-37-187-156.eu/manuals/SoundBot%20Speaker/SoundBot%20SB571%20Speaker.pdf