Get a field label instead of value using the api
I assume you mean a drop-down field? You then need to do another lookup on the OptionValue to get the label, e.g. from the api explorer:

    $result = civicrm_api3('OptionValue', 'get', [
      'return' =&gt; ["label"],
      'option_group_id' =&gt; "custom_marital_status",
      'value' =&gt; "S",
    ]);


gives you

"is_error": 0,
    "version": 3,
    "count": 1,
    "id": 866,
    "values": [
        {
            "id": "866",
            "label": "Single"
        }
    ]