str_replace() with associative array

$text = strtr($text, $array_from_to)

By the way, that is still a one dimensional "array."

$array_from_to = array (
    'from1' => 'to1',
    'from2' => 'to2'
);

$text = str_replace(array_keys($array_from_to), $array_from_to, $text);

The to field will ignore the keys in your array. The key function here is array_keys.