The vowel sounds in Russian words get reduced depending on their position in relation to the stressed vowel. Here, 3 different positions are distinguished:
- the stressed vowel;
- the vowel in the syllable directly preceding the stressed syllable;
- all the rest of the vowels in the word.
Vowels in position 1 are always pronounced as they are, and also they are loud, distinct, and long.
In positions 2 and 3 the result of the reduction is like this:
- the letters <а> and <о> become [ɐ] in position 2 and [ə] in position 3: барабан [bərɐˈban], молоко [məlɐˈko];
- as for the letters <у>, <е>, and <и>, each of them has the same sound in positions 2 and 3: for <у> it's [ʊ] – кусать [kʊˈsatʲ] (position 2), муравей [mʊrɐˈvʲej] (position 3).
For <е> and <и> the reduced sound is always [ɪ]: веселиться [vʲɪsʲɪˈlʲit͡sːə], миллион [mʲɪlʲɪˈon].
Now, your words
Examples: клавиатура and биржа , for both of these words they have the same IPA in the area of the и, yet sound completely different.
You probably simply didn't notice the difference in the IPA symbols for <и> in these two words, but the difference is there, and the difference is important, although graphically it's just a mere dot over i.
биржа, <и> is stressed, so it's pronounced like [i] and sounds very much like the English <ее> in meet or feel:
клавиатура, <и> is in the second syllable before the stressed <у>, so it is in position 3 and that's why it is pronounced as [ɪ] (note, there's no dot over it), that's the sound found in the English words sit, pin, or big:
IPA is a set of technical symbols, that's why all their graphic elements (like the presence/absence of the dot over i) are functional and cannot be neglected, or else inevitable confusion will arise.