Here is the code:

<?php
// Write a program that prints the numbers from 1 to 100. 
// But for multiples of three print "Fizz" instead of the number and for the multiples of five print "Buzz". 
// For numbers which are multiples of both three and five print "FizzBuzz".

    echo "<p>Howdy Tim, Here are your numbers :)</p>\n";
    
    for($i = 1; $i <= 100; $i++){
    	// for readability I prefere to print the number with the word and explanation to the right
        if( (($i % 3) == 0) && (($i % 5) != 0) ){ 
            echo "<p class='fizz'>$i -- <b>Fizz</b> is a multiple of 3</p>\n";
        }
        else if( (($i % 5) == 0) && (($i % 3) != 0) ){
            echo "<p class='buzz'>$i -- <b>Buzz</b> is a multiple of 5</p>\n";
        }
        else if( (($i % 5) == 0) && (($i % 3) == 0) ){
            echo "<p class='fizzbuzz'>$i -- <b>FizzBuzz</b> is a multiple of 3 and 5</p>\n";
        }
        else {
            echo "<p>$i</p>";
        }
    }
    
    echo "<p>All Done!</p>\n";
?>

Here is the actual output:

Howdy Tim, Here are your numbers :)

1

2

3 -- Fizz is a multiple of 3

4

5 -- Buzz is a multiple of 5

6 -- Fizz is a multiple of 3

7

8

9 -- Fizz is a multiple of 3

10 -- Buzz is a multiple of 5

11

12 -- Fizz is a multiple of 3

13

14

15 -- FizzBuzz is a multiple of 3 and 5

16

17

18 -- Fizz is a multiple of 3

19

20 -- Buzz is a multiple of 5

21 -- Fizz is a multiple of 3

22

23

24 -- Fizz is a multiple of 3

25 -- Buzz is a multiple of 5

26

27 -- Fizz is a multiple of 3

28

29

30 -- FizzBuzz is a multiple of 3 and 5

31

32

33 -- Fizz is a multiple of 3

34

35 -- Buzz is a multiple of 5

36 -- Fizz is a multiple of 3

37

38

39 -- Fizz is a multiple of 3

40 -- Buzz is a multiple of 5

41

42 -- Fizz is a multiple of 3

43

44

45 -- FizzBuzz is a multiple of 3 and 5

46

47

48 -- Fizz is a multiple of 3

49

50 -- Buzz is a multiple of 5

51 -- Fizz is a multiple of 3

52

53

54 -- Fizz is a multiple of 3

55 -- Buzz is a multiple of 5

56

57 -- Fizz is a multiple of 3

58

59

60 -- FizzBuzz is a multiple of 3 and 5

61

62

63 -- Fizz is a multiple of 3

64

65 -- Buzz is a multiple of 5

66 -- Fizz is a multiple of 3

67

68

69 -- Fizz is a multiple of 3

70 -- Buzz is a multiple of 5

71

72 -- Fizz is a multiple of 3

73

74

75 -- FizzBuzz is a multiple of 3 and 5

76

77

78 -- Fizz is a multiple of 3

79

80 -- Buzz is a multiple of 5

81 -- Fizz is a multiple of 3

82

83

84 -- Fizz is a multiple of 3

85 -- Buzz is a multiple of 5

86

87 -- Fizz is a multiple of 3

88

89

90 -- FizzBuzz is a multiple of 3 and 5

91

92

93 -- Fizz is a multiple of 3

94

95 -- Buzz is a multiple of 5

96 -- Fizz is a multiple of 3

97

98

99 -- Fizz is a multiple of 3

100 -- Buzz is a multiple of 5

All Done!