Re: phrasing slur in piano staff

[Noeck]

Dear Ming,

I would also do what Simon suggested. If you need additional voices
temporarily, you can still do so and continue the first voice with your
phrasing slur and add a new voice next to it:

\version "2.18.2"
\language "english"
global = {
  \key f \major
  \numericTimeSignature
  \time 6/8
  \partial 8
  \tempo 4=100
}
 mux = { \global
  c'8^\( | <f'a'>4. <<{f'8 g'8 a'8 |bf'4. }\\{f'4.~ f'4.}>> <f'a'>4\) %m
  <<
    {<d'g'>8^\( | f'8. e'16 f'8 } % starting slur here, say voice 1
    \new Voice {s8 c'4.}      % additional voice 2
  >>
  <e'g'>4 <e'g'c''>8 |%m          % still the same voice 1
  <<
    {<f'c''>4.~q4\)}              % still the same voice 1
    \new Voice {c'4. d'4}         % additional voice 3
  >> <e'bf'>8 |%m
}
\score { \mux }

Cheers,
Joram