Book Cambridge pronunciation in Use Elementary, at Section B, item A3c
In some words there are silent letters (letters with no sound). In listen, t is silent.
listen 6 letters, 5 sounds
+---+---+---+---+---+---+
| l | i | s | t | e | n |
+---+---+---+---+---+---+
| 1 | 2 | 3 | - | 4 | 5 |
+---+---+---+---+---+---+
How to explain, "listen" has 5 sounds while its pronunciation is /ˈlɪsn/?
Related link https://www.oxfordlearnersdictionaries.com/definition/english/listen_1?q=listen
How to explain, "listen" has 5 sounds while its pronunciation is /ˈlɪsn/?
The word is pronounced as two syllables, not a single syllable ending in a consonant cluster, so you need to have a second vowel sound in your transcription. As the table shows, that vowel sound corresponds to the "e" in the spelling.
As with many unstressed vowels in English, it can reasonably be transcribed as a schwa: /ˈlɪsən/
The consonant cluster "sn" does occur in English, but only at the start of syllables - i.e. it needs to be followed by a vowel sound. The similar cluster "sm" occurs in writing at the end of syllables, notably in the suffix "-ism", but is generally pronounced as an additional syllable, /...ɪzəm/
"Listen" actually can have either 5 or 4 sounds, but the difference is not important in English. So don't worry too much about it.
Both [ˈlɪsn] and [ˈlɪsən] are possible pronunciations: they are phonetically different because in the first one, the consonant sound [s] is followed directly by the consonant sound [n], while in the second, there is a brief vowel sound [ə], called schwa, between them.
If we say the word as [ˈlɪsn], the consonant [n] is syllabic (unlike the [n] in a word like "snail") and an optional way to mark that a consonant is syllabic in the International Phonetic Alphabet is to put a short vertical line below it, like this: [lɪsn̩].
Even though syllabic consonants can occur in some English words, their use is optional: a syllabic consonant can always be replaced by a schwa followed by a non-syllabic consonant without changing the meaning of a word. Since there is no contrast, a "phonemic" transcription (a transcription that only shows contrasts that can make a meaningful difference) will generally include the schwa: /ˈlɪsən/.
By convention, slash marks are supposed to be reserved for phonemic transcriptions, whereas phonetic transcriptions are supposed to be surrounded by square brackets like [lɪsn̩].
Here are references I provided when answering Are ə before l/m/n/r optional? on ELU Stack Exchange: two blog posts by the phonetician John Wells:
In the first of these, Wells says
Syllabic consonants are never categorically required in English. There is always an alternative pronunciation available, with ə and a nonsyllabic consonant.
Base on the information given by IMSoP, with Cambridge dictionary
https://dictionary.cambridge.org/pronunciation/english/listen
/ˈlɪs.ən/
There are 5 sounds.