<?php
$tests = array(
'First line<br>second line<br>third line',
'First line <br>second line <br>third line',
'First line<br> second line<br> third line',
'First line <br> second line <br> third line',
'First line <br> second line<br>third line',
'First line <br> second line <br>third line',
'First line<br>second line <br> third line',
'First line <br> second line<br> third line',
'First line<br> second line <br> third line',
'First line<br/>second line<br/>third line',
'First line <br/>second line <br/>third line',
'First line<br/> second line<br/> third line',
'First line <br/> second line <br/> third line',
'First line <br/> second line<br/>third line',
'First line <br/> second line <br/>third line',
'First line<br/>second line <br/> third line',
'First line <br/> second line<br/> third line',
'First line<br/> second line <br/> third line',
'First line<br />second line<br />third line',
'First line <br />second line <br />third line',
'First line<br /> second line<br /> third line',
'First line <br /> second line <br /> third line',
'First line <br /> second line<br />third line',
'First line <br /> second line <br />third line',
'First line<br />second line <br /> third line',
'First line <br /> second line<br /> third line',
'First line<br /> second line <br /> third line',
'First line<br class="hide-on-mobile" /> second line <br class="hide-on-mobile" /> third line',
);
foreach ( $tests as $test ) {
echo preg_replace( '/(\s)?<br(.*?)>(\s)?/', ' ', $test ), PHP_EOL;
}