Check new telephone number when there's an error (#1608)

app/views/merge_requests/confirm_telephone_number.html.erb

@@ -21,7 +21,12 @@
       <% if @merge_request.absorbing_organisation.phone.present? %>
         <%= f.govuk_radio_buttons_fieldset(:telephone_number_correct, legend: nil) do %>
           <%= f.govuk_radio_button :telephone_number_correct, true, checked: @merge_request.telephone_number_correct?, label: { text: "This telephone number is correct" }, link_errors: true %>
-          <%= f.govuk_radio_button :telephone_number_correct, false, checked: @merge_request.new_telephone_number.present?, label: { text: "Enter a new phone number" } do %>
+          <%= f.govuk_radio_button(
+            :telephone_number_correct,
+            false,
+            checked: (@merge_request.new_telephone_number.present? || @merge_request.errors.key?(:new_telephone_number)),
+            label: { text: "Enter a new phone number" },
+          ) do %>
             <%= f.govuk_text_field :new_telephone_number, label: { text: "Telephone number" }, width: "two-thirds" %>
           <% end %>
           <%= f.hidden_field :page, value: "confirm_telephone_number" %>