For streaming your android phone's primary camera and reading the stream in OpenCV

rtsp_stream_to_device.py

# conda create -n env python=3.6
# pip install opencv-python # this is important because you need ffmpeg enabled

import cv2
import numpy as np
import time

import os
# For UDP Speed instead of default TCP
os.environ["OPENCV_FFMPEG_CAPTURE_OPTIONS"] = "rtsp_transport;udp"

my_android_phone = "rtsp://192.168.0.100:8080/h264_pcm.sdp"

vcap = cv2.VideoCapture(my_android_phone)


def run(cap):
    while True:
        ret, frame = cap.read()
        if not ret:
            print("Frame is empty")
            time.sleep(0.5)
            continue

        cv2.imshow('VIDEO', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break


if __name__ == "__main__":
    run(vcap)
    vcap.release()
    cv2.destroyAllWindows()

Forgot to mention. Please install the Android app from the play store: IP Webcam.
You can find it here Link