Link to custom field breaks output

Hi

I would like to build a link to a value (phone number) coming from a custom field [phone]. This is, what I initially tried:Expecting the visible output 024 261 11 11 (linked to 4124261111) I unfortunately only manage to get something «rotten» like

24 261 11 11">024 261 11 11.

Having a look at the HTML code, I can see there's obviously something going on with the «span» tag (I don't even use).
To ensure my «tel:-link creations» don't infere with the regular articles anywhere code, I tried with the following
and with output="value"
Since I use two " inside the a-attribute, «output value» is not working neither.

What's my mistake?

Thank you