Александр

<?php

function date_period_grid($start, $end)
{
    $start = new DateTime($start);
    $end   = new DateTime($end);
    
    $interval = $end->diff($start);

    $days   = $interval->days;
    $months = $interval->y * 12 + $interval->m;
    $years  = intval($end->format('Y')) - intval($start->format('Y'));
	
    if ($years > 1) {
        $period = new DatePeriod($start, new DateInterval('P1Y'), $years);
        $format = 'Y';
    } elseif ($months > 1) {
        $period = new DatePeriod($start, new DateInterval('P1M'), $months);
        $format = 'm.Y';
    } else {
        $period = new DatePeriod($start, new DateInterval('P1D'), $days);
        $format = 'd.m.Y';
    }
    
    $result = [];
    foreach ($period as $date) {
        $result[] = $date->format($format);
    }
    
    return $result;
}

date_period_grid('2012-07-01', '2015-11-01'); 
// => ['2012', '2013', '2014', '2015']

date_period_grid('2015-01-01', '2015-11-01');
// => ['01.2015', '02.2015', ..., '11.2015']

date_period_grid('2015-10-01', '2015-11-01');
// => ['01.10.2015', '02.10.2015', ..., '01.11.2015']