Transfer html tags to specific characters

I'm trying to transfer the following HTML to a little bit tricky form using php, as shown below:

<dd>abc<br />def<br />ghi</dd>

↓

abc
def
ghi

Say <dd>abc<br />def<br />ghi</dd> is defined at $strRet. How can I use some combinations of str_replace and/or preg_replace functions to modify to the specific format?

Thanks in advance,

via Chebli Mohamed