I have 2 dates in PHP, how can I run a foreach loop to go through all of those days?

Requires PHP5.3:

$begin = new DateTime('2010-05-01');
$end = new DateTime('2010-05-10');

$interval = DateInterval::createFromDateString('1 day');
$period = new DatePeriod($begin, $interval, $end);

foreach ($period as $dt) {
    echo $dt->format("l Y-m-d H:i:s\n");
}

This will output all days in the defined period between $start and $end. If you want to include the 10th, set $end to 11th. You can adjust format to your liking. See the PHP Manual for DatePeriod.

This also includes the last date

$begin = new DateTime( "2015-07-03" );
$end   = new DateTime( "2015-07-09" );

for($i = $begin; $i <= $end; $i->modify('+1 day')){
    echo $i->format("Y-m-d");
}

If you dont need the last date just remove = from the condition.

Converting to unix timestamps makes doing date math easier in php:

$startTime = strtotime( '2010-05-01 12:00' );
$endTime = strtotime( '2010-05-10 12:00' );

// Loop between timestamps, 24 hours at a time
for ( $i = $startTime; $i <= $endTime; $i = $i + 86400 ) {
  $thisDate = date( 'Y-m-d', $i ); // 2010-05-01, 2010-05-02, etc
}

When using PHP with a timezone having DST, make sure to add a time that is not 23:00, 00:00 or 1:00 to protect against days skipping or repeating.