In standard Spanish, one can tell the pronunciation of a word from its spelling, but not vice versa, as phonemes sometimes can be represented in more than one way, but a given letter is consistently pronounced.
ɪn stˈændɚd spˈænɪʃ, wˈʌn kæn tˈɛl ðə pɹənˌʌnsɪˈeɪʃən əvə wˈɜːd fɹʌm ɪts spˈɛlɪŋ, bˌʌt nˌɑːt vˈaɪs vˈɜːsə, æz fˈoʊniːmz sˈʌmtaɪmz kæn biː ɹˌɛpɹᵻzˈɛntᵻd ɪn mˈoːɹ ðɐn wˈʌn wˈeɪ, bˌʌt ɐ ɡˈɪvən lˈɛɾɚɹ ɪz kənsˈɪstəntli pɹənˈaʊnst.