I am looking at the: simpleRTK2B – Starter Kit LR 
I would love to also have the option to connect to the simpleRTK2B via my phone’s bluetooth (use the simpleRTK2B as an external GPS). Is that possible to use more than 1 radio (LR + Bluetooth module  )? Looks like the simpleRTK2B only as 1 XBee socket. Is there a way?
It is possible, but unfortunately today the second xbee device needs to be wired manually to the arduino rails.
Would that basically be the same steps as outlined here?: https://www.ardusimple.com/simplertk2b-connection-via-bluetooth/
Looks like in the video you use SparkFun’s Bluetooth modem – https://www.sparkfun.com/products/12576
As this is more of an edge case, would the SparkFun Bluetooth modem make more sense here, as it seems to have more exposed headers rather than having to deal with the XBee socket of the Ardusimple Bluetooth module? – https://www.ardusimple.com/product/bluetooth-module/
Sure, bes both options are ok. The only difference is that our bluetooth comes pre-configured for serial port operation, the one from Sparkfun you will have to configure it with AT commands.
Could you please deliver the minimum wiring required for the bluetooth, the LR radio and the wifi NTRIP Master to work?
Is it just TX RX and Ground, as I prefer to power those modules with separate power to keep a low noise on the power for the ZED-F9P.
To enable TX1 and RX1 on the arduino rails, you also need to connect IOREF to 3V3_OUT for example.
I got things working on my end. Here is a simple wiring diagram I did: https://hillert.blogspot.com/2020/03/ardusimple-simplertk2b-with-long-range.html
As I am a bit of a novice, could you explain the function of the IOREF pin? I read its definition for Arduino but I am a bit confused. As I already connected the 3V3_OUT to the Bluetooth Module, shouldn’t that be sufficient? (Feels redundant)
the connection looks good. the ioref defines the voltage level of tx and rx pins in the arduino rails. if IOREF = 3.3V, the rx,rx pins will be references to this value
would it be the same when I want to use NTRIP Master as RTK client together with the Bluetooth module?
UART 1 → BT module manuall wired as described above → all protocols?
UART 2 → NTRIP Master on XBEE socket with NMEA (as client)
Thank´s and stay healthy!