Thanks @fzinken! I could pair my phone with “My Osmc” add-on!!!
I have still a problem: I can stream audio to the TV set but the sound doesn’t go to the analog audio output of the raspi. The audio output is properly configured, if I play music or videos, the audio goes to both, TV and audio output. My goal is to hear music without using the TV.
I took some time to read this thread and at least 15 persons have the same problem, but none of the answers helped me 
I’ve tried to configure ALSA settings as proposed by @Alistair_Richardson without success:
amixer -c 0 cset numid=3 1
Also setting setting hdmi_ignore_edid_audio=1 in /boot/config.txt does not make any effect (taken from ALSA audio through 3.5mm jack instead of HDMI - #7 by b3n_ja_m1n)
The interesting thing is that when playing music over BT, changing any setting in audio output (only analog, only HDMI, both, alsa) makes no effect, the sound goes always to HDMI. Tests were done with these versions:
Kodi 17.6
Osmc 2018.12-1
a2dp-app-osmc 1.1.3