Guten Tag!
Several PhonerLite's versions/modifications ago (about half year ago) the PhonerLite's Opus codec appeared info 18 kbps, but it's sound quality was like 48-50 kbps (compared with LinPhone 48 kHz 50 kbps best quality Opus and with lower quality WB G722/Speex). Now PhonerLite's quality is 18 kbps. But LinPhone hasn't some PhonerLite's good features. 
Is it possible to make PhonerLite's version with Opus 48-50 kbps or with both speeds/bitrates for Opus? Thnx!

I with my friends use Linphone and PhonerLite several years for speech, not music, of course identical program on both sides.
Current PhonerLite with Opus-18 or G722 WB or Speex WB (quality: this like this) transmits sound "S" is like "Sh"near"F"("Ph"), sound "Z"("Th") is like about "Zh", but half year ago PhonerLite or current Linphone hasn't this problem with Opus. We tested these "S" and "Z"("Th") sounds with PhonerLite now and earlier, with different hardwares/internet-providers any sides, so it's not hardware and not internet and not SIP-provider problem.
You wrote: "Opus codec automatically choses right data rate and quality needed for the provided signal" - but why PhonerLite's Opus half year ago versions-modifications automatically chose factually 48(50) for speech PhonerLite-2-PhonerLite (but now it's factually 18)? Of course I remember that half year ago PhonerLite offered only Opus-18 option, but factually it was 48(50) sound quality like Linphone.
So if use current PhonerLite's codecs assortment - it distorts speech because they trim high frequencies, but if Opus-48(50) quality - it's like You talk with companion near You.
http://cdni.wired.co.uk/1920x1280/o_r/opuscodec.jpg
For real quality music is fullband stereo Opus 128 and higher, for real quality speech - mono fullband Opus 40-128 kbps: Opus-48(50) is enough. Also Skype use about it.
Opus-18 is WB quality near Speex WB or near G.722 WB - not-super-wideband.

PhonerLite had and has only Opus-18 option, not 48(50), but half years ago and early PhonerLite's versions/modifications worked for talking/speech with selected Opus-18 like it's Opus-48(50) quality.
So, wanting for Opus-48(50) quality or additional option for Phonerlite's next version/modification.
If only Opus-18 option, no Opus-48(50) option now and in early versions, so there is and was no ability to configure to use 48 kHz Opus, but Opus-48(50) worked with about half year ago or early versions. I don't remember version/modification number when change and when PhonerLite lost Opus-48 quality.

I found where to change sampling rate (was 16000 Hz ~ Opus 18 kbps). Thanks, You holp me. Now codec list shows Opus 50 kbps.
Was some problem because possible different translations/meanings. 'll test later, 'll write if problem even now.

I can't reproduce any difference in sound quality when using 48 kHz and G.722 here.
Can you take at Options/Configuration/Sound if you have enabled options there that may cause the problem.

There are no plans to to do any automatic sample rate change if special codecs are used. Sorry.