Parse TextGrid phone intervals.
        
        This method parses the phone intervals in a TextGrid to extract each
        phone and each phone's start and end times in the audio recording. For
        each phone, it instantiates the class Phone(), with the phone and its
        start and end times as attributes of that class instance.

def parse_phones(self):
        """Parse TextGrid phone intervals.
        
        This method parses the phone intervals in a TextGrid to extract each
        phone and each phone's start and end times in the audio recording. For
        each phone, it instantiates the class Phone(), with the phone and its
        start and end times as attributes of that class instance.
        
        """
        phones = []
        
        for i in self.phone_intervals:
            start = float(i[i.index('xmin = ')+7:
                            i.index('xmin = ')+12].strip('\t').strip('\n'))
            end = float(i[i.index('xmax = ')+7:
                          i.index('xmax = ')+12].strip('\t').strip('\n'))
            phone = i[i.index('\"')+1:i.index("$")]
            phones.append(Phone(phone, start, end))
            
        return phones