How to change xml attributes with PHP using input from forms?

How to change xml tag attribute taken from an input with PHP? I have an xml phonebook and i want to make a web app that users would be able to change xml attributes with input from html forms. What kind of functions or methods should i use? I cant figure out a way for this to work by myself. Thank you for help in advance.

<PhoneBook>
<Title>TRSA</Title>
<Menu Name="Informational">
<Unit Name="Name Surname" Phone1="476" Phone2="8 888 88 888" Phone3="62811" default_photo="Resource:"/>
<Unit Name="John Johnson" Phone1="412" Phone2="" Phone3="62812" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="481" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="481" Phone2="" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="427" Phone2="" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="414" Phone2="" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="414" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="410" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
</Menu>
<Menu Name="Administration">
<Unit Name="Carl Johnson" Phone1="413" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="450" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="344" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="484" Phone2="" Phone3="52110" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="465" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson " Phone1="522" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
</Menu>
<Menu Name="Control">
<Unit Name="Carl Johnson" Phone1="475" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="525" Phone2="" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="448" Phone2="" Phone3="22222" default_photo="Resource:"/>
</Menu>
<Menu Name="Quality">
<Unit Name="Carl Johnson" Phone1="415" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="524" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="404" Phone2="8 888 88 888" Phone3="22222" default_photo="Resource:"/>
<Unit Name="Carl Johnson" Phone1="416" Phone2="" Phone3="22222" default_photo="Resource:"/>
</Menu>
</PhoneBook>