SELECT 
  field_id 
FROM 
  cscart_profile_fields 
WHERE 
  1 
  AND `section` = "C" 
  AND `profile_show` = "Y" 
  AND `profile_required` = "Y" 
  AND `field_name` = "phone"

Query time 0.00022

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.004452,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_profile_fields",
          "access_type": "ref",
          "possible_keys": ["field_name", "profile_show"],
          "key": "field_name",
          "key_length": "98",
          "used_key_parts": ["field_name"],
          "ref": ["const"],
          "loops": 1,
          "rows": 2,
          "cost": 0.004452,
          "filtered": 52.83018875,
          "index_condition": "cscart_profile_fields.field_name = 'phone'",
          "attached_condition": "cscart_profile_fields.section = 'C' and cscart_profile_fields.profile_show = 'Y' and cscart_profile_fields.profile_required = 'Y'"
        }
      }
    ]
  }
}