OK, my Table looks a lot like yours:

  Order   part    part description
  number  number
  ------  ------  ----------------
  Aa      123     phone
  Aa      456     accessory
  Aa      185     accessory
  Aa      844     misc document
  Bg      454     phone
  Bg      888     phone
  Bg      928     accessory
  Cp      988     accessory
  Cp      909     misc document

I wrote 3 Queries.  The first adds a sequence number to each record with
a given part number.

[Q_Seq] SQL:
  SELECT Parts.[Order number], [Parts]![part number]
  & [Parts]![part description] AS Stuff,
  Count(Parts_1.[part number]) AS [CountOfpart number]
  FROM Parts INNER JOIN Parts AS Parts_1
  ON Parts.[Order number] = Parts_1.[Order number]
  WHERE (((Parts_1.[part number])<=[Parts].[part number]))
  GROUP BY Parts.[Order number],
  [Parts]![part number] & [Parts]![part description]
  ORDER BY [Parts]![part number]
  & [Parts]![part description];

The third column contains the sequence number.

[Q_Seq]
  Order     Stuff               CountOfpart number
  number
  ------    ------------------  ------------------
  Aa        123phone            1
  Aa        185accessory        2
  Bg        454phone            1
  Aa        456accessory        3
  Aa        844misc document    4
  Bg        888phone            2
  Cp        909misc document    1
  Bg        928accessory        3
  Cp        988accessory        2

The 2nd Query crosstabs them in the order specified by the generated
sequence number.  If you have more than four of any of them, there will
be additional columns in the Query Datasheet View.  I showed only the
first 3 of them.  You can limit how many you have by setting some criteria.

[Q_Seq_Crosstab]
  TRANSFORM Min(Q_Seq.Stuff) AS MinOfStuff
  SELECT Q_Seq.[Order number]
  FROM Q_Seq
  GROUP BY Q_Seq.[Order number]
  PIVOT Q_Seq.[CountOfpart number];

[Q_Seq_Crosstab]
  Order   1                2               3             ...
  number
  ------  ---------------- -------------   ------------
  Aa      123phone         185accessory    456accessory  ...
  Bg      454phone         888phone        928accessory  ...
  Cp      909misc document 988accessory

Then the 3rd Query piles the numbered columns together into a combined
field.  If you expect more than 4 values for any one [Order number],
you'll need to include them here.

[Q_Cat]
  SELECT Q_Seq_Crosstab.[Order number],
  [Q_Seq_Crosstab]![1] & " "
  & [Q_Seq_Crosstab]![2] & " "
  & [Q_Seq_Crosstab]![3] & " "
  & [Q_Seq_Crosstab]![4] AS Cat
  FROM Q_Seq_Crosstab
  ORDER BY Q_Seq_Crosstab.[Order number];

[Q_Cat]
  Order  Cat
  number
  ------ ---------------------------------------------------
  Aa     123phone 185accessory 456accessory 844misc document
  Bg     454phone 888phone 928accessory
  Cp     909misc document 988accessory

If you don't like the order I used, you should modify the SQL for
[Q_Seq] to generate those numbers differently.

  -- Vincent Johns <vjohns@alumni.caltech.edu>
  Please feel free to quote anything I say here.