I have heard of those two sentences as containing the 36 French phonemes:

Au loin un gosse trouve, dans la belle nuit complice, une merveilleuse et fraîche jeune campagne.

Il faut déjà que vous sachiez que les bords de telles rues ne sont qu’un peu glissants le matin à Zermatt.

but I didn’t count and identify the phonemes myself. These two sentences just appear in various studies and corpus with the mention that they contain all 36 French phonemes.

I’ve just googled them and this website (not a scientific website though) confirms this.

The sentence that contains almost all phonemes with the IPA transcription:

Au loin un gosse trouve, dans la belle nuit complice, une merveilleuse et fraîche jeune campagne.

/ o lwɛ̃ œ̃ gɔsə tʁuvə – dɑ̃ la bɛlə nɥi kɔ̃.plisə – ynə mɛːʁ.vɛjøz‿e fʁɛːʃə – ʒœnə kɑ̃.paɲə /

Vowels are in bold characters. A few phonemes are missing:

• /ɑ/ (as in drap, pâte). As mentioned in the Wiktionary, in Metropolitan French, /ɑ/ is often replaced by /a/. The distinction is however present in Belgian French and in Quebec French.
• /ŋ/ (as in bingo, parking) which is found in imported words.
• /h/ (as in Ha ! Ha !) may appear in a few interjections.

Quebec French may make a difference between /ɛː/ and /ɛ/, but it is mostly lost in all other regions. This sentence contains both.

Also it does not contain any internal mid-central vowels /ə/, so I’ve added those which may appear between words, which are more or less pronounced depending on the region.

Regarding: “The first sentence lacks [ɑ] (a distinct phoneme from [a] in most French dialects), [h] (only found in a few interjections) and [ŋ] (found in some English imports, not merged with [ng] by all speakers). Apart from the lack of [h], I think there are speakers for which it works.”

According to: https://easypronunciation.com/en/french-letters-pronunciation-ipa-chart

[ɑ] is now pronounced as [a] by most French speakers in France.

Here is their phonetic conversion of:

Au loin un gosse trouve, dans la belle nuit complice, une merveilleuse et fraîche jeune campagne.

o lwɛ̃ œ̃ ɡɔs tʁuv, dɑ̃ la bɛl nɥi kɔ̃plis, yn mɛʁvɛjøz e fʁɛʃ ʒœn kɑ̃paɲ.

or

o lwɛ̃ œ̃ ɡɔs tʁuːv, dɑ̃ la bɛl nɥi kɔ̃plis, yn mɛʁvɛjøz e fʁɛʃ ʒœn kɑ̃paɲ.

In English the phonetic conversion for [a] is the sound of the “a” in “trap” and [ɑ] is the sound of “a” in the word “bra.” I think French tends to use the “a” is in “bra” although you may notice that the second “a” in “campagne” (kɑ̃paɲ) may use the sound of “a” as in the word “trap.”

Honestly the difference in some of the French vowel sounds can be very difficult to master for American English speakers.

I translated the sentence as follows:
“In the distance a child finds, in the companionship of a beautiful night, a wonderful and fresh young countryside.”

Ma soeur Denise brosse ses longs cheveux gris avec un peigne d’or, et elle cueille des fruits mûrs pour sa jolie bouche rose.

Was presented with this in my French class that discussed the pronunciation of the vowel phonemes, we were assigned it to practice the sentence in front of a mirror. Pre-selfie days. I have been searching for this one and found this thread. Now contributing.