hugo-theme-lowtech/layouts/partials/contact/telephone.html

{{- with .Site.Data.contact.telephone -}}
{{- $protocol := "tel" -}}
{{- $tel := . -}}
{{- $telWithProtocol := print $protocol ":" (replace $tel " " "") -}}
<a
  class="tel obfuscate"
  data-link="{{ range $index := seq (sub (len $telWithProtocol) 1) 0}}{{ substr $telWithProtocol $index 1}}{{ end }}"
>{{ range $index := seq (sub (len $tel) 1) 0}}{{ substr $tel $index 1}}{{ end }}</a>
{{- end -}}