Here is a great algorithm for finding easter – I wrote it in C, you’ll have to make it a php function. Pass in the year, it returns the month and the day. Keep in mind, this only works for thw western church easter. Some of the Eastern Orthodox use a different method of reckoning.
void RomanEaster( int year, int *month, int *day )
{
int y, j, k, h, m, n, p, q, r, s, u, v, w, x, z;
y = year;
j = y % 19; /* this is a modulus operator */
k = y / 100;
h = y % 100;
m = k / 4;
n = k % 4;
p = (k+8) / 25;
q = (k-p+1) / 3;
r = (19*j+k-m-q+15) % 30;
s = h / 4;
u = h % 4;
v = (32+2*n+2*s-r-u) % 7;
w = (j+11*r+22*v) / 451;
x = (r+v-7*w+114) / 31;
z = (r+v-7*w+114) % 31;
*month = x;
*day = z+1;
return;
}