TennisGame1.php

<?php

class TennisGame1 implements TennisGame
{
    private $m_score1 = 0;
    private $m_score2 = 0;

    private $player1Name = '';
    private $player2Name = '';

    private $score_map = [
        0 => 'Love',
        1 => 'Fifteen',
        2 => 'Thirty',
        3 => 'Forty',
    ];

    public function __construct($player1Name, $player2Name)
    {
        $this->player1Name = $player1Name;
        $this->player2Name = $player2Name;
    }

    public function wonPoint($playerName)
    {
        if ('player1' === $playerName) {
            $this->m_score1++;
        } else {
            $this->m_score2++;
        }
    }

    private function isEven()
    {
        if ($this->m_score1 === $this->m_score2) {
            return true;
        }
        return false;
    }

    private function getEvenScore()
    {
        if ($this->m_score1 < 3) {
            return $this->score_map[$this->m_score1] . '-All';
        }
        return 'Deuce';
    }

    private function isAdvantageOrWin()
    {
        if ($this->m_score1 >= 4 || $this->m_score2 >= 4) {
            return true;
        }
        return false;
    }

    private function getAdvantageOrWin()
    {
        $diff = abs($this->m_score1 - $this->m_score2);

        if ($this->m_score1 > $this->m_score2) {
            if ($diff === 1) {
                return 'Advantage player1';
            }
            return 'Win for player1';
        }

        if ($diff === 1) {
            return 'Advantage player2';
        }
        return 'Win for player2';
    }

    private function getOtherScore()
    {
        return $this->score_map[$this->m_score1] . '-' . $this->score_map[$this->m_score2];
    }

    public function getScore()
    {
        if ($this->isEven()) {
            return $this->getEvenScore();
        }

        if ($this->isAdvantageOrWin()) {
            return $this->getAdvantageOrWin();
        }

        return $this->getOtherScore();
    }
}

Refactored https://github.com/emilybache/Tennis-Refactoring-Kata/blob/master/php/TennisGame1.php.