Rp-pppoe ISP-Simulation

I replaced a Telekom Speedport Smart 4 router with an x68 OpenWrt device. The registration with the ISP works great thanks to this tutorial:

But now I would like to be able to use my phone again. The phone is connected to the speedport, but the speedport wants to establish a pppoe connection. I have configured rp-pppoe as suggested in various tuts. Unfortunately I can't get a connection with the speedport.

config pppoe_server
        option ac_name 'access-concentrator-name'
        list service_name 'service-name1'
        list service_name 'service-name2'
        option maxsessionsperpeer '0'
        option localip '192.168.2.1'
        option maxsessions '64'
        option optionsfile '/etc/ppp/pppoe-server-options'
        option randomsessions '1'
        option unit '0'
        option offset '0'
        option timeout '60'
        option mss '1468'
        option sync '0'
        option interface 'lan'
        option firstremoteip '192.168.3.2'
# PPP options for the PPPoE server
# LIC: GPL
#require-pap
require-chap
login
lcp-echo-interval 10
lcp-echo-failure 2
mru 1492
mtu 1492
usepeerdns

Do I need to create a ppp interface? How do I assign the VLAN ID 7?

Why do you need to use the Speedport?
If it is only for the wifi, then you can make it a dumbAP and connect it behind the OpenWrt.

Telephony

That's what I did. Works like a charm. But without telephony.

It seems that the Speedport needs a connection via pppoe on its WAN port for telephony to work. There is also an error message stating that the speedport has no connection to the internet.

Then you don't need to create a pppoe server on the OpenWrt, rather to bridge the wan side ethernet tagged with vlan 7 to one lan port which is connecting to the Speedport's wan port.
There is an example in the same page but for adsl. However the principle is the same and if you have questions we can help you.

Only a partial help, but fritzboxes can be configured to use one of their LAN ports as WAN (speedports likely as well) AND fritzOS offers configurations without pppoe on the wan side... Given that telekom always seems to use pppoe such a mode might not be supported in speedports. Then again second hand fritzboxen are relatively cheap...